The present invention relates to an adhesive composition, and more specifically a hot melt polyurethane adhesive composition.
There are a number of commercial laminates and materials which must be bonded together using equipment wherein rapid cure rate is critical. However, this improved cure rate cannot come at the expense of a decrease in thermal stability.
One way to improve cure rate is to utilize catalysts such as organo tin and bismuth catalysts, e.g., dibutyl tin dilaurate, dimethyl tin distearate, zinc stearate and mixtures thereof. The use of these catalysts, however, typically results in the loss of thermal and viscosity stability. An alternative is suggested in EP 0 668 302 wherein it is proposed to use a 2,2'dimorpholino-ethyl ether or di(2,6-alimethylmorpholinoethyl) ether catalyst to catalyze polyurethane reactive hot melt adhesives. Another alternative is suggested in U.S. Pat. No. 4,515,846 to McKinney et al., and relates to a carpet backing composition comprising a urethane composition, a thermoplastic composition and two catalysts. The catalysts are a conventional catalyst (e.g., dibutyl tin dilurate) and a delayed action heat activated catalyst (e.g., metal salts of dicarboxylic acids, acid salts of amines, and imidazole derivatives).
U.S. Pat. No. 4,524,104 to Hagio proposes an adhesive composition comprising an acrylic copolymer having NCO-reactive groups, a blocked polyisocyanate and a catalyst such as 1,8-diaza-bicyclo(5,4,0)undec-7-ene (DBU). The composition is useful as a pressure sensitive adhesive. There is, however, no disclosure of using an unblocked polyisocyanate.
U.S. Pat. No. 5,558,917 to Markusch et al. relates to a polyurethane carpet backing comprising polyisocyanates of less than about 2.4, an isocyanate group content of 25 to 30 percent and a urethane group content of 2 to 6 percent and comprising polymethylene poly(phenylisocyanate), from about 5 to 25 percent of 4,4'-methylene bis(phenyloisocyanate), and from about 20 to 50 percent of 2,2'- and 2,4'-methylene bis(phenyl-isocyanate).
There, however, remains a need for a catalyst that provides for rapid curing of aliphatic hot melt polyurethane compositions derived from unblocked polyisocyanates without adversely affecting thermal or viscosity stability or both.